1. Field of the Invention
The present invention relates to a communication apparatus, and more specifically to a communication apparatus for use in a short-distance wireless communication system. The present invention also relates to a method and a computer program for use in such a communication apparatus.
2. Description of the Background Art
Recently, along with a growth of short-distance wireless communication technologies, it is required in various fields to utilize PANs (Personal Area Networks) relying upon such grown communication technologies.
For example, traditionally, infrared transmission is utilized for a communication instrument for remote control manipulation of television (TV) receivers and other devices. However, the infrared transmission has a strong directivity. Thus, the user has to direct a remote control handset to an object to be manipulated. If an obstacle exists on the transmission path from the handset to the object, no transmission may be available.
Instead, application of a short-distance radio communication device to remote control makes remote control available even when an obstacle intervenes on the transmission path.
As a typical standard for short-distance wireless communication form, the IEEE (Institute of Electrical and Electronics Engineers, Inc.) 802.15.4 has been presented. The IEEE 802.15.4-based communication uses a 2.4 GHz bandwidth, which is called the ISM band (Industrial Scientific Medical Band) and shared with, for example, microwave ovens and wireless LANs (Local Area Networks) The communication using the IEEE 802 has a radiowave output comparatively weaker than, for example microwave ovens and wireless LANs.
Thus, under the situation where other devices such as microwave oven and wireless LAN emit radiowaves, the communication with the IEEE 802.15.4 may suffer radiowave interference from those devices and fail in connection.
For example, Japanese patent laid-open publication No. 2005-142815 discloses a communication technology available even under radiowave interference as described above.
Communication between wireless communication devices generally needs the same channels shared by both sender and receiver communication devices. Normally, before communication starts, the sender and receiver communication devices negotiate with each other about communication channels according to various methods.
The Japanese '815 publication also teaches a technology in which, if communication fails due to radiowave interference, the sender communication device changes a communication channel to be used for retransmitting data. Specifically, the receiver communication device scans all channels while waiting for responses, and the sender communication device in turn sends, before data transmission, multiple times a preamble including a destination address. In this way, the receiver communication device uses a channel on which it received the preamble to proceed to data communication.
The conventional art in the Japanese '815 publication however has problems as described below when applied to a remote control communication instrument, for instance.
As described above, according to the technology in the Japanese '815 publication, the receiver communication device has to scan all channels as well as frame, or byte, synchronization. Furthermore, the sender communication device has to send a preamble multiple times. Thus, the conventional art, if applied to a remote control communication method, has a problem in that good responsiveness cannot be offered.
In addition, in a TV remote control system, for example, a TV receiver set works also as a receiver communication device for remote control. The application of the conventional art to the TV receiver set acting as a remote control receiver device allows its power consumption to be reduced. However, the TV set itself consumes a large power in its units other than the remote control circuitry. As a result, such a TV receiver set fails to significantly save the whole power.
The above-mentioned problems arise not only in the case of a remote control communication device using a short-distance wireless communication but also in other cases, such as a PAN system with short-distance wireless communication and a wireless communication with a plurality of channels.